1. Field of the Invention
The invention relates to free-flowing transparent polyamide molding compositions having substantially unimpaired mechanical properties.
2. Discussion of the Background
Transparent copolyamides are generally distinguished over other materials by good low-temperature impact strength and good chemical resistance; in addition, they have high light transparency together with an amorphous structure, which provides good shrinkage behavior. Such materials can be used to produce molded articles having superior properties. However, transparent polyamide compositions have a high melt viscosity, which makes processing them considerably more difficult than other types of molding compositions. For example, thin-walled injection-molded articles can be produced from transparent copolyamides only with difficulty.
Plastics can usually be rendered more free-flowing by lowering the number average molecular weight. However, this generally also results in a significant impairment of the mechanical properties. In the case of polyamides, the impact strength in particular is drastically reduced by lowering the number average molecular weight of the polymer below a critical value.
Another way of improving the flow behavior of plastics is to add so-called flow improvers. Low molecular weight additives are frequently employed for this purpose. In the case of transparent plastics, however, additives of this type frequently result in a loss in transparency or in the formation of deposits in the mold during processing.
CA-A 2,039,136 describes amorphous polyamides having improved flow behavior which are obtained by adding certain types of carbon black to the polyamides. DE-A 3728 334 describes the improvement in the flow of amorphous polyamides by addition of polyolefins grafted with maleic anhydride. A. Siegmann et al. (Polymer, 1985, 26(9), 1325-1330) were able to reduce the melt viscosity of amorphous polyamides by the addition of liquid crystalline polyesters. In all of these cases however, the additives destroy the transparency of the amorphous polyamides.
C.F. Frihart et al. (Plast. Copd. 1990, 13(3), 109-110) were able to reduce the melt viscosity of an amorphous polyamide by adding at least 1% by weight of an additional amorphous polyamide based on a dimeric fatty acid (C36-dicarboxylic acid). However, this procedure results in a significant reduction in the modulus of elasticity of the blend.
U.S. Pat. No. 3,442,975 suggests that a polyethyleneimine-PA 6 graft copolymer can be used as flow aid for PA 6. However, this is a crystalline, opaque polyamide, and the mixture of polyethyleneimine-PA 6 graft copolymer with PA 6 is also opaque.
The object of the present invention is to develop free-flowing transparent polyamide molding compositions which do not have the above-mentioned disadvantages of the prior art, and whose mechanical properties, in particular tensile strength, modulus of elasticity, flexural strength and impact strength, are only slightly impaired compared to the unmodified transparent polyamides. This is achieved by blending the transparent polyamide with a graft copolymer formed from a branched polyamine and polyamide-forming monomers.
The molding composition of the present invention comprises the following components:
I) from 50 to 99 parts by weight, preferably from 75 to 98 parts by weight and particularly preferably from 85 to 97 parts by weight, of a transparent polyamide, and
II) from 1 to 50 parts by weight, preferably from 2 to 25 parts by weight and particularly preferably from 3 to 15 parts by weight, of a graft copolymer prepared from the following monomers:
a) from 0.5 to 25% by weight, preferably from 1 to 20% by weight and particularly preferably from 1.5 to 16% by weight, based on the graft copolymer, of a branched polyamine having at least 4, preferably at least 8 and particularly preferably at least 11 nitrogen atoms and having a number average molecular weight Mn of at least 146 g/mol and preferably of at least 500 g/mol, and
b) polyamide-forming monomers selected from lactams, xcfx89-aminocarboxylic acids and/or equivalent combinations of diamine and dicarboxylic acid, where the sum of the parts by weight of I) and II) is 100.
Transparent polyamides are known (Kunststoffhandbuch [Plastics Handbook] 3/4, Editors G. W. Becker and G. Braun, pp. 803 ff., Carl Hanser Verlag Munich, Vienna, 1998). Transparent polyamides which are suitable for the purposes of the invention are also described, for example, in the following publications: U.S. Pat. No. 2,742,496, CH-B-480 381, CH-B-679 861, DE-A-22 25 938, DE-A-26 42 244, DE-A-27 43 515, DE-A-29 36 759, DE-A-27 32 928, DE-A-43 10 970, EP-A-0 053 876, EP-A-0 271 308, EP-A-0 313 436, EP-A- 0 725 100 and EP-A-0 725 101.
The transparent polyamides used in accordance with the present invention, which can also be in the form of copolyamides, are prepared, for example, from the following monomers:
branched or unbranched aliphatic diamines having 6 to 14 carbon atoms, for example, 1,6-hexamethylenediamine, 2-methyl-1,5-diaminopentane, 2,2,4- or 2,4,4-trimethylhexamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine or 1,12-dodecamethylenediamine;
cycloaliphatic diamines having 6 to 22 carbon atoms, for example, 4,4xe2x80x2-diaminodicyclohexylmethane, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodicyclohexylmethane, 4,4xe2x80x2-diaminodicyclohexylpropane, 1,4-diaminocyclohexane, 1,4-bis(aminomethyl)cyclohexane, 2,6-bis(aminomethyl)norbomane or 3-aminomethyl-3,5,5-trimethylcyclohexylamine;
araliphatic diamines having 8 to 22 carbon atoms, for example, m- or p-xylylenediamine or bis(4-aminophenyl)propane;
branched or unbranched aliphatic dicarboxylic acids having 6 to 22 carbon atoms, for example, adipic acid, 2,2,4- or 2,4,4-trimethyladipic acid, azelaic acid, sebacic acid or 1,12-dodecanedioic acid;
cycloaliphatic dicarboxylic acids having 6 to 22 carbon atoms, for example, cyclohexane-1,4-dicarboxylic acid, 4,4xe2x80x2-dicaboxydicyclohexylmethane, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-dicarboxydicyclohexylmethane, 4,4xe2x80x2-dicarboxydicyclohexylpropane and 1,4-bis(carboxymethyl)cyclohexane;
araliphatic dicarboxylic acids having 8 to 22 carbon atoms, for example, 4,4xe2x80x2-diphenylmethanedicarboxylic acid;
aromatic dicarboxylic acids having 8 to 22 carbon atoms, for example isophthalic acid, tributylisophthalic acid, terephthalic acid, 1,4-, 1,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, diphenic acid or 4,4xe2x80x2-oxybis(benzoic acid),
lactams having 6 to 12 carbon atoms or the corresponding aminocarboxylic acids, such as, for example, 6-caprolactam, 6-aminocaproic acid, caprylolactam, xcfx89-amipocaprylic acid, xcfx89-aminoundecanoic acid, laurolactam or xcfx89-aminododecanoic acid.
Examples of transparent polyamides which can be used in accordance with the invention are as follows:
the copolyamide made from terephthalic acid and the isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine,
the polyamide made from isophthalic acid and 1,6-hexamethylenediamine,
the copolyamide made from a mixture of terephthalic acid/isophthalic acid and 1,6-hexamethylenediamine,
the copolyamide made from isophthalic acid, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodicyclohexylmethane and laurolactam or caprolactam,
the polyamide or copolyamide made from 1,12-dodecanedioic acid, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodicyclohexylmethane and, if desired, laurolactam or caprolactam,
the copolyamide made from isophthalic acid, 4,4xe2x80x2-diaminodicyclohexylmethane and laurolactam or caprolactam,
the polyamide made from 1,12-dodecanedioic acid and 4,4xe2x80x2-diaminodicyclohexylmethane,
the copolyamide made from a terephthalic acid/isophthalic acid mixture, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodicyclohexylmethane and laurolactam.
The branched polyamine can be, for example, any of the following classes of polyamines:
dendrimers, for example,
((H2Nxe2x80x94(CH2)3)2Nxe2x80x94(CH2)3)2-N(CH2)2-N((CH2)2xe2x80x94N((CH2)3xe2x80x94NH2)2)2 (DE-A-196 54179)or tris(2-aminoethyl)amine, N, N-bis(2-aminoethyl)-Nxe2x80x2,Nxe2x80x2-bis{2-{bis(2-aminoethyl)amino}ethyl}-1,2-ethanediamine or
3,15-bis(2-aminoethyl)-6, 12-bis{2-{bis(2-aminoethyl)amino}ethyl}-9-{2{bis{2-bis(2-aminoethyl)amino}ethyl}amino}ethyl}-3,6,9,12,15-pentaazaheptadecane-1,17-diamine (J. M. Warakomski, Chem. Mat. 1992, 4, 1000-1004);
branched polyethyleneimines, which are obtainable by polymerization of aziridines (Houben-Weyl, Methoden der Organischen Chemie {Methods of Organic Chemistry}, Volume E20, pages 1482-1487, Georg Thieme Verlag Stuttgart, 1987) and which generally have the following amino group distribution:
from 25 to 46% of primary amino groups,
from 30 to 45% of secondary amino groups and
from 16 to 40% of tertiary amino groups.
In the preferred case, the polyamine has a number average molecular weight Mn of at most 20,000 g/mol, particularly preferably of at most 10,000 g/mol and particularly preferably of at most 5000 g/mol.
The polyamide-forming monomers employed can be any of the monomers mentioned above for the transparent polyamide, in particular lactams and/or xcfx89-aminocarboxylic acids. Particular preference is given to xcex5-caprolactam, xcfx89-aminoundecanoic acid and/or laurolactam, the latter primarily if the transparent polyamide comprises a substantial proportion of copolymerized laurolactam. However, it is also possible to employ an equivalent combination of diamine and dicarboxylic acid, if desired, together with a lactam and/or an xcfx89-aminocarboxylic acid.
In one possible embodiment, the graft copolymer may be prepared with the additional use of an oligocarboxylic acid selected from 0.015 to about 3 mol % of dicarboxylic acid and 0.01 to about 1.2 mol % of tricarboxylic acid, in each case based on the sum of the moles of the other polyamide-forming monomers. In this connection, each monomer in the combination of diamine and dicarboxylic acid is considered individually.
If a dicarboxylic acid is used, the amount added to the graft copolymer is preferably from 0.03 to 2.2 mol %, particularly preferably from 0.05 to 1.5 mol %, very particularly preferably from 0.1 to 1 mol % and in particular from 0.15 to 0.65 mol %. If a tricarboxylic acid is used, the amount added to the graft copolymer is preferably from 0.02 to 0.9 mol %, particularly preferably from 0.025 to 0.6 mol %, very particularly preferably from 0.03 to 0.4 mol % and in particular from 0.04 to 0.25 mol %. The concomitant use of the oligocarboxylic acid significantly improves the solvent and hydrolysis resistance of the graft copolymer.
The oligocarboxylic acid employed can be any desired di- or tricarboxylic acid having 6 to 24 carbon atoms, for example adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, trimesic acid and/or trimellitic acid.
In addition, if desired, aliphatic, alicyclic, aromatic, aralkyl- and/or alkylaryl-substituted monocarboxylic acids having 3 to 50 carbon atoms, such as, for example, lauric acid, unsaturated fatty acids, acrylic acid or benzoic acid, can be employed as a regulator. By means of these regulators, the concentration of amino groups can be reduced without changing the shape of the molecule.
The graft copolymers according to the invention can be prepared by various processes. One possibility is to initially introduce the lactam or xcfx89-aminocarboxylic acid and polyamine together and to carry out the polymerization or polycondensation. The oligocarboxylic acid can be added either at the beginning or during the reaction. However, a preferred two-step process comprises first carrying out the lactam cleavage and prepolymerization in the presence of water (alternatively, the corresponding xcfx89-aminocarboxylic acids or diamines and dicarboxylic acids are employed and prepolymerized directly). In the second step, the polyamine is added, while any oligocarboxylic acid used concomitantly is metered in before, during or after the prepolymerization. The mixture is then held under reduced pressure at temperatures of from 200 to 290xc2x0 C. and polycondensed in a stream of nitrogen or under reduced pressure.
A further preferred process comprises the hydrolytic degradation of a polyamide to a prepolymer and the simultaneous or subsequent reaction with the polyamine. Preference is given to polyamides in which the end group difference is approximately zero or in which any oligocarboxylic acid used concomitantly has already been copolycondensed. However, the oligocarboxylic acid can also be added at the beginning or during the degradation reaction.
These processes allow the preparation of ultra-highly branched polyamides having acid numbers of less than 40 mmol/kg, preferably less than 20 mmol/kg and particularly preferably less than 10 mmol/kg. After a reaction time of only from one to five hours at temperatures of from 200xc2x0 C. to 290xc2x0 C., approximately complete conversion is achieved.
If desired, this can be followed, in a further process step, by holding the graft copolymer thus formed under vacuum for a number of hours. Fir example, this step may last at least four hours, preferably at least six hours and particularly preferably at least eight hours at a temperature of from 200 to 290xc2x0 C. After an induction period of several hours, an increase in the melt viscosity of the polymer is then observed, which is probably attributable to a reaction of amino end groups with one another, together with elimination of ammonia and the formation of crosslinks.
If it is not desired to continue the reaction to completion in the melt, the graft copolymer can also be post-condensed in the solid phase by conventional methods for polyamides.
The transparent polyamide and the graft copolymer can be mixed with one another by any conventional method. For example, the mixing may be carried out in the melt in a compounding unit.
The molding composition according to the invention can also contain conventional auxiliaries and additives used in transparent polyamides, for example, flame retardants, stabilizers, plasticizers, glass fibers or other polymers which do not impair the transparency of the molding composition. The amount of all additives is in total a maximum of 40 parts by weight, preferably a maximum of 30 parts by weight and particularly preferably a maximum of 20 parts by weight.
Moldings can be produced from the molding composition by any conventional method, for example by extrusion, blow molding, thermoforming and, in particular, injection molding. The molding composition according to the present invention is also excellently suited for the extrusion coating of any desired surface.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.